Why does an empty method report allocating bytes? #2402
Description
Hello,
I noticed some weird results from our benchmarks when we moved our app from .net framework to .net 6.0.
Methods that should not allocate at all were reporting allocations of 8 bytes.
I've investigated and in trying to make a nice simple reproducible example I discovered that an empty method reports allocating 8 bytes
// * Summary *
BenchmarkDotNet v0.13.7, Windows 10 (10.0.19045.3208/22H2/2022Update)
12th Gen Intel Core i7-1265U, 1 CPU, 12 logical and 10 physical cores
.NET SDK 7.0.400
[Host] : .NET 6.0.21 (6.0.2123.36311), X64 RyuJIT AVX2
Job-NXFHSY : .NET 6.0.21 (6.0.2123.36311), X64 RyuJIT AVX2
Runtime=.NET 6.0 InvocationCount=64 IterationCount=10
LaunchCount=1 WarmupCount=8
| Method | Mean | Error | StdErr | StdDev | Min | Q1 | Median | Q3 | Max | Op/s | Rank | Allocated |
|------------ |-------:|-------:|-------:|-------:|-------:|-------:|-------:|-------:|-------:|---------:|-----:|----------:|
| EmptyMethod | 0.0 ns | 0.0 ns | 0.0 ns | 0.0 ns | 0.0 ns | 0.0 ns | 0.0 ns | 0.0 ns | 0.0 ns | Infinity | 1 | 8 B |
I've include the very basic set up I have below
Class Library defining the benchmarks - Target framework net6.0, single class
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Configs;
using BenchmarkDotNet.Environments;
using BenchmarkDotNet.Jobs;
namespace BenchmarkTests
{
[MemoryDiagnoser]
[Config(typeof(Config))]
[RankColumn]
[AllStatisticsColumn]
public class Benchmarks
{
[Benchmark]
public void EmptyMethod()
{
}
private class Config : ManualConfig
{
public Config()
{
AddJob(
new Job(EnvironmentMode.Default, RunMode.Short)
{
Environment = { Runtime = CoreRuntime.Core60 },
Run = { InvocationCount = 64, WarmupCount = 8, IterationCount = 10 }
});
}
}
}
}
Console App that runs the benchmarks - Target framework net6.0, single class to define entry point
using BenchmarkDotNet.Running;
namespace BenchmarkTests.Runner
{
internal class Program
{
static void Main(string[] args)
{
BenchmarkRunner.Run<Benchmarks>();
}
}
}